1. Field of the Invention
The invention relates to a Global Position System (GPS) receiver for receiving and processing GPS signals comprising means for receiving and processing Digital Audio Broadcast (DAB) signals.
2. Description of the Related Art
Such a receiver is known from e.g., the article xe2x80x9cMobile Satellite Communications for Consumersxe2x80x9d by Mr. G. K. Noreen, published in Microwave Journal, November, 1991, pages 24-34. The known receiver shows the use of a DAB receiver and a GPS receiver in one receiver housing. The advantages of having both single-to-multipoint transmission capabilities and position information at hand are extensively explained therein.
However, the use of complete receivers for DAB and GPS signals in one housing is not only costly, but may also give rise to mutual interferences in the processing of the received DAB and GPS signals.
It is an object of the invention to reduce the costs of implementing such receiver while maintaining, or even improving, performance of both DAB and GPS features. Therefore, a GPS receiver for receiving and processing GPS signals comprising means for receiving and processing Digital Audio Broadcast (DAB) signals, according to the invention is characterized by a receiver front end, a mixer stage, filtering means and analog-to-digital converter means being coupled to digital DAB and GPS signal paths, includes DAB signal eliminating means for selectively eliminating DAB signals from said digital GPS signal path.
The invention is based on the recognition that proper correlation of GPS signal does not necessarily require haveing the GPS signals available continuously or fully separated from DAB signals. This allows to either interrupt the processing of GPS signals during the data carrying signal segments of a DAB signal, hereinafter also referred to as non-zero DAB data segments, or to tolerate the occurrence of DAB signals in the GPS signal path of the receiver, therewith enabling to combine the processing of GPS signals with a processing of DAB signals and to use certain receiver circuitry in common for both GPS and DAB processing. By applying the above measure according to the invention certain RF circuitry may be used for both GPS and DAB signal processing, whereas, at least after digitization, GPS signal processing is fully separated from DAB signal processing. This allows for a reduction in the costs of implementation while preventing mutual interferences between the GPS and DAB signal processing from occurring.
Preferably a GPS receiver, according to the invention, is being characterized by a voltage-controlled oscillator supplying a tuneable local oscillator signal to the mixer stage, said DAB signal eliminating means comprising control means coupled to a DAB demodulator included in said DAB signal path and providing a control signal to the voltage-controlled oscillator as well as to a switching device, said switching device being coupled between the analog-to-digital converter means on, the one hand and, said control means tuning the receiver to receive GPS signals, and simultaneously controlling the switch to disconnect the filtering means from the GPS signal path and to connect the filtering means to the DAB signal path at the occurrence of non-zero level DAB data segments.
By applying this measure, the receiver is switched from a GPS reception mode to a DAB reception mode and vice versa, dependent of the occurrence of non-zero level data carrying segments, respectively, zero level NULL symbols, in the DAB signals, therewith allowing to use the complete receiver circuitry for the reception and processing of both DAB and GPS signals. This shared use of circuitry allows further reductions in the price of manufacturing.
Another embodiment of a GPS receiver according to the invention is characterized by the receiver front-end comprising mutually separated DAB and GPS receiver front-ends, respectively coupled to a DAB and GPS mixer stage, outputs of these DAB and GPS mixer stages being coupled through, respectively, a DAB and GPS filtering device to an adder, an output thereof being coupled to said DAB and GPS signal paths, said DAB and GPS mixer stages providing a frequency conversion of the DAB and GPS signals into mutually different frequency ranges.
By applying this measure, the selective elimination of DAB signals from said digital GPS signal path is obtained by a mutual separation in frequency. Non-zero DAB signals are therewith blocked from entering into the GPS signal path.
Preferably such embodiment is characterized by DAB channel selection means for selecting a DAB channel having a frequency range located beyond the frequency range of the GPS signals, said DAB channel selection means being controlled by a DAB channel selection control device.
This measure allows for a further suppression of DAB signals within the frequency range of the GPS signals while obtaining an improvement of the DAB channel selection.
Yet another preferred embodiment of a GPS receiver according to the invention, is characterized by signal replica means for regenerating received DAB signals from a decoded DAB signal, as well as compensation means for subtracting the regenerated DAB signals from the GPS signals in the GPS signal path.
This measure results in a feed-forward compensation of DAB signals in the GPS signal path, which with a proper adjustment in phase and amplitude of the DAB replica signal, allows to fully eliminate DAB signals from the GPS signal path.